docs: tiny typo in 'first_concepts.rst'
docs: tiny typo in 'first_concepts.rst'

Testing Done:
ran the ci.sh. Output: [== CI SUCCESS ==]

Reiewed at https://rbcommons.com/s/twitter/r/376/

dturner-tw/pants,sid-kap/pants,wisechengyi/pants,pantsbuild/pants,peiyuwang/pants,kwlzn/pants,jsirois/pants,gmalmquist/pants,dgomez10/xanon,manasapte/pants,landism/pants,di0spyr0s/pants,gmalmquist/pants,areitz/pants,qma/pants,mateor/pants,dgomez10/xanon,jessrosenfield/pants,15Dkatz/pants,scode/pants,pantsbuild/pants,15Dkatz/pants,twitter/pants,kwlzn/pants,qma/pants,digwanderlust/pants,sameerparekh/pants,laurentgo/pants,areitz/pants,laurentgo/pants,gmalmquist/pants,sid-kap/pants,foursquare/pants,dbentley/pants,cevaris/pants,manasapte/pants,lahosken/pants,megaserg/pants,foursquare/pants,UnrememberMe/pants,TansyArron/pants,wisechengyi/pants,gmalmquist/pants,tejal29/pants,UnrememberMe/pants,digwanderlust/pants,peiyuwang/pants,tdyas/pants,ericzundel/pants,slyphon/pants,fkorotkov/pants,sameerparekh/pants,lahosken/pants,ericzundel/pants,pgroudas/pants,mateor/pants,digwanderlust/pants,megaserg/pants,lahosken/pants,baroquebobcat/pants,sameerparekh/pants,twitter/pants,peiyuwang/pants,jessrosenfield/pants,cevaris/pants,Gabriel439/pants,pantsbuild/pants,baroquebobcat/pants,di0spyr0s/pants,peiyuwang/pants,areitz/pants,digwanderlust/pants,UnrememberMe/pants,peiyuwang/pants,mateor/pants,Gabriel439/pants,scode/pants,TansyArron/pants,kslundberg/pants,Gabriel439/pants,qma/pants,twitter/pants,scode/pants,pgroudas/pants,foursquare/pants,wisechengyi/pants,wisechengyi/pants,jessrosenfield/pants,ericzundel/pants,dturner-tw/pants,square/pants,foursquare/pants,lahosken/pants,tejal29/pants,jtrobec/pants,sameerparekh/pants,dbentley/pants,UnrememberMe/pants,landism/pants,15Dkatz/pants,sid-kap/pants,15Dkatz/pants,tdyas/pants,tdyas/pants,dturner-tw/pants,baroquebobcat/pants,twitter/pants,ity/pants,jessrosenfield/pants,slyphon/pants,slyphon/pants,manasapte/pants,twitter/pants,foursquare/pants,ericzundel/pants,sameerparekh/pants,di0spyr0s/pants,foursquare/pants,ity/pants,foursquare/pants,square/pants,areitz/pants,kwlzn/pants,pombredanne/pants,megaserg/pants,manasapte/pants,baroquebobcat/pants,tdyas/pants,jtrobec/pants,sameerparekh/pants,cevaris/pants,pgroudas/pants,qma/pants,scode/pants,fkorotkov/pants,kslundberg/pants,manasapte/pants,pantsbuild/pants,dgomez10/xanon,15Dkatz/pants,benjyw/pants,benjyw/pants,fkorotkov/pants,sid-kap/pants,ity/pants,kslundberg/pants,slyphon/pants,fkorotkov/pants,TansyArron/pants,ericzundel/pants,mateor/pants,jsirois/pants,kslundberg/pants,pombredanne/pants,dgomez10/xanon,pombredanne/pants,tdyas/pants,kslundberg/pants,square/pants,wisechengyi/pants,baroquebobcat/pants,UnrememberMe/pants,cevaris/pants,dturner-tw/pants,fkorotkov/pants,peiyuwang/pants,dturner-tw/pants,mateor/pants,qma/pants,ity/pants,sid-kap/pants,mateor/pants,lahosken/pants,benjyw/pants,ity/pants,UnrememberMe/pants,UnrememberMe/pants,gmalmquist/pants,landism/pants,dturner-tw/pants,gmalmquist/pants,tejal29/pants,kslundberg/pants,dbentley/pants,dgomez10/xanon,pantsbuild/pants,cevaris/pants,baroquebobcat/pants,twitter/pants,sid-kap/pants,ericzundel/pants,jtrobec/pants,benjyw/pants,tdyas/pants,lahosken/pants,kwlzn/pants,pantsbuild/pants,qma/pants,benjyw/pants,laurentgo/pants,jsirois/pants,dbentley/pants,dbentley/pants,dturner-tw/pants,jessrosenfield/pants,landism/pants,ericzundel/pants,dbentley/pants,manasapte/pants,dgomez10/xanon,digwanderlust/pants,megaserg/pants,tejal29/pants,baroquebobcat/pants,pombredanne/pants,landism/pants,pantsbuild/pants,sameerparekh/pants,laurentgo/pants,tejal29/pants,gmalmquist/pants,megaserg/pants,kwlzn/pants,slyphon/pants,areitz/pants,fkorotkov/pants,manasapte/pants,15Dkatz/pants,pombredanne/pants,cevaris/pants,foursquare/pants,benjyw/pants,kwlzn/pants,TansyArron/pants,pombredanne/pants,peiyuwang/pants,dgomez10/xanon,lahosken/pants,dgomez10/xanon,landism/pants,areitz/pants,kwlzn/pants,UnrememberMe/pants,areitz/pants,slyphon/pants,jessrosenfield/pants,twitter/pants,wisechengyi/pants,kslundberg/pants,twitter/pants,scode/pants,dgomez10/xanon,lahosken/pants,TansyArron/pants,peiyuwang/pants,pgroudas/pants,tdyas/pants,jtrobec/pants,qma/pants,tdyas/pants,slyphon/pants,UnrememberMe/pants,baroquebobcat/pants,TansyArron/pants,pgroudas/pants,pombredanne/pants,twitter/pants,Gabriel439/pants,di0spyr0s/pants,jtrobec/pants,sid-kap/pants,mateor/pants,square/pants,jtrobec/pants,wisechengyi/pants,landism/pants,mateor/pants,ity/pants,fkorotkov/pants,jtrobec/pants,tdyas/pants,15Dkatz/pants,pgroudas/pants,wisechengyi/pants,laurentgo/pants,cevaris/pants,landism/pants,scode/pants,15Dkatz/pants,megaserg/pants,digwanderlust/pants,wisechengyi/pants,di0spyr0s/pants,di0spyr0s/pants,foursquare/pants,megaserg/pants,di0spyr0s/pants,laurentgo/pants,jessrosenfield/pants,dbentley/pants,fkorotkov/pants,scode/pants,Gabriel439/pants,TansyArron/pants,Gabriel439/pants,dgomez10/xanon,baroquebobcat/pants,dgomez10/xanon,Gabriel439/pants,ericzundel/pants,benjyw/pants,ity/pants